1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to controlling access point transmit power.
2. Introduction
A wireless communication network may be deployed over a geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, macro access points (e.g., each of which provides service via one or more cells) are distributed throughout a macro network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the macro network.
As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance. To supplement conventional network access points (e.g., to provide extended network coverage), small-coverage access points (e.g., low power access points) may be deployed to provide more robust indoor wireless coverage or other coverage to access terminals inside homes, enterprise locations (e.g., offices), or other locations. Such small-coverage access points may be referred to as, for example, femto cells, femto access points, Home NodeBs, Home eNodeBs, or access point base stations. Typically, such small-coverage access points are connected to the Internet and the mobile operator's network via a DSL router or a cable modem. For convenience, small-coverage access points may be referred to as femto cells or femto access points in the discussion that follows.
In a co-channel or shared carrier deployment of femto cells such as Home Node Bs, there is a need to protect non-Closed Subscriber Group access terminals (also denoted as non-allowed access terminals or macro access terminals) from interference from Home NodeBs by limiting the transmit power of the Home NodeBs for pilot, overhead, data, and other channels. This transmit power control may be referred to as Home NodeB power calibration. One goal of a transmit power calibration algorithm is to strike a balance between Home NodeB coverage provided to served access terminals (e.g., home access terminals) and limiting the interference impact on non-served access terminals (e.g., macro access terminals or other femto access terminals).
Some conventional transmit power calibration schemes are based on measurements made by a downlink receiver (e.g., a Network Listen Module) at the Home NodeB. This calibration is based on the assumption that nearby home access terminals and nearby macro access terminals will see the same or similar RF conditions as the Network Listen Module. This assumption is not fully accurate, however. Consequently, Network Listen Module-based transmit power calibration suffers from two mismatch conditions.
First, there may be an RF mismatch condition. For example, a Home NodeB placed near a window may see significantly higher macro interference than a home access terminal which may be predominantly away from the window. As another example, a Home NodeB placed in a basement may see significantly lower macro interference than a home access terminal which is predominantly in a higher floor.
Second, there may a deployment mismatch condition. For example, the Network Listen Module is unaware of the macro access terminal traffic surrounding the Home NodeB deployment. A Home NodeB deployed near a busy street corner in a small apartment may affect more macro access terminals than one deployed deep inside a suburban home. This mismatch creates an inaccurate power setting for the Home NodeB in the sense that the power setting may create too much interference for macro users. This interference could lead to excessive inter-frequency handovers or call drops (e.g., when the Home NodeB is placed near a window or near a busy street corner) or could result in inadequate coverage for home access terminals (e.g., when the Home NodeB is placed in a basement or when the Home NodeB is used in a ranch house).
In view of the above, there is a need for effective techniques for protecting macro cell users and other non-allowed users from interference from femto cells while still providing adequate coverage for allowed femto cell users.